To conserve power, it is important to reduce power losses in transistors that are used, for example, in direct current (DC) to DC converters. In a metal oxide semiconductor field effect transistor (MOSFET) device, and in particular in the class of MOSFETs known as power MOSFETs, power losses can be reduced by reducing the device's on-resistance (Rdson).
Breakdown voltage provides an indication of a device's ability to withstand breakdown under reverse voltage conditions. Because breakdown voltage is inversely related to Rdson, it is adversely affected when Rdson is reduced. To address this problem, super junction (SJ) power MOSFETs, which include alternating p-type and n-type regions below the active regions of the device, were introduced. The alternating p-type and n-type regions in a SJ power MOSFET are ideally in charge balance (Qp=Qn) so that those regions deplete one another under a reverse voltage condition, thereby enabling the device to better withstand breakdown.